JP2994441B2 - Living eye size measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method of observing interference fringes to determine an axial length of a living eye as a dimension from a first measurement target surface to a second measurement target surface. The present invention relates to an improvement of a living eye measuring apparatus capable of measuring a chamber depth, a lens thickness, and the like without contact.

(Prior Art) Conventionally, a living body that measures the axial length, anterior chamber depth, lens thickness, and the like as dimensions from a first measurement target surface to a second measurement target surface of a living eye using ultrasonic waves. Eye dimension measuring devices are known.

This living eye measurement device projects ultrasonic waves from the front of the eye, draws reflected waves on the front surface of the cornea, the front surface of the lens, the back surface of the lens, and the fundus surface on a CRT, and captures the echogram drawn on the CRT. Is measured.

By the way, since a conventional living eye size measuring device has a measurement accuracy of about ± 0.2 mm, for example, it is necessary to determine the power of an IOL (Intraocular Lens) using the axial length obtained as a result of the measurement. However, the measurement accuracy of the axial length was insufficient.

In addition, the conventional ultrasonic eye size measurement device using ultrasonic waves,
Since the probe must be brought into contact with the living eye during the measurement, it is necessary to take precautionary measures such as infection, which is troublesome.

Therefore, in recent years, there has been proposed a dimension measuring apparatus for a living eye capable of measuring an axial length, an anterior chamber depth, a lens thickness, and the like in a non-contact manner by observing interference fringes.

FIG. 5 shows an example of a living eye size measuring apparatus used for measuring the axial length of an eye.
et al. (OPTICS LETTER VOL.13 NO.3 PP.186-188 (Mar
ch 1988) Technology described in the Optical Society of America).

This living eye size measuring device is roughly composed of a semiconductor laser 1, a collimator lens 2, two parallel flat plates 3, 4, a beam splitter 5, a condenser lens 6, and an imaging camera 7.

The laser light emitted from the semiconductor laser 1 is converted into a parallel light beam by the collimating lens 2 and guided to the two parallel flat plates 3 and 4. A parallel light flux (referred to as a light flux) that has passed through the two parallel flat plates 3 and 4 is guided as convergent light to the fundus 9 of the living eye 8 via the beam splitter 5, is reflected by the fundus 9, and is substantially parallel light flux (plane wave). ) Is emitted from the living eye 8. The emitted plane wave is reflected by the reflecting surface 10 of the beam splitter 5 in the direction in which the condenser lens 6 exists,
The light is condensed by the condenser lens 6 and guided to the imaging camera 7. Also, a part of the parallel light flux passing through the parallel plane plate 3 is:
The light is reflected by the parallel flat plate 4 and returns to the parallel flat plate 3 as a reflected light flux (referred to as a light flux). The reflected light is again reflected by the parallel flat plate 3 and passes through the parallel flat plate 4 and the beam splitter 5 to the cornea 11 of the living eye 8. Be guided. The reflected light reflected by the cornea 11 is guided to the beam splitter 5 as divergent light (spherical wave), reflected by the reflection surface 10 in the direction in which the condenser lens 6 exists, and condensed by the condenser lens 6. It is led to the camera 7. In FIG. 5, reference numeral 12 denotes a light-receiving sensor for monitoring the amount of light of the semiconductor laser 1.

In this conventional device, the distance d between the parallel flat plate 3 and the parallel flat plate 4 is variable, the refractive index of a substance existing between the parallel flat plate 3 and the parallel flat plate 4 is n, and the refractive index of the intraocular substance is n. Assuming that the refractive index is N and the axial length of the eye obtained by the measurement (the distance from the vertex of the cornea 11 to the fundus 9) is X, the distance d is adjusted so as to satisfy the equation of nd = NX. The optical path length becomes equal, and interference fringes are observed by the camera 7. Therefore, by obtaining the distance d when the interference fringes are observed as a measured value, the axial length X can be obtained.

(Problems to be Solved by the Invention) However, in a living eye size measuring device that measures the axial length of an eye by observing interference fringes, the luminous flux reflected from the corneal surface is substantially spherical, whereas Since the light flux reflected from the surface is a substantially plane wave, the number of interference fringes becomes very large as the distance from the apex of the cornea to the peripheral portion increases, and there is a problem that good observation of the interference fringes cannot be performed. In particular, the reflected light from the fundus is not actually about a plane wave due to the refractive power of the eye,
In addition, it was difficult to read the number of interference fringes because the interference fringes gathered at the center.

Further, in this living eye size measuring device, the optical axes of the condenser lens 6 and the camera 7 must be accurately aligned with the living eye 8, but there is a problem that the alignment is extremely troublesome. .

The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to easily perform good observation of interference fringes and to measure the measurement accuracy without being affected by the refractive power of the eye to be examined. It is an object of the present invention to provide a living eye size measuring apparatus which can be expected to improve the size of a living eye.

(Means for Solving the Problems) In order to achieve the above object, a living eye size measuring apparatus according to the present invention projects a light beam having a short coherence length onto a living eye, and a first measurement target surface of the living eye. A size measuring apparatus for measuring a dimension from the first measurement target surface to the second measurement target surface based on an interference between a reflected light flux from the object and a reflected light flux from a second measurement target surface, wherein the coherence length is Is split into a light beam projected onto the first measurement target surface and a light beam projected onto the second measurement target surface by an optical path splitting member, and is again optically synthesized by an optical path synthesizing member. A light beam projecting unit for projecting light to a living eye, wherein a wavefront shape of a light beam reflected from the first measurement target surface and a wavefront shape from the second measurement target surface are provided between the optical path splitting member and the optical path combining member. The wavefront shape of the reflected light flux Providing a refractive power correction optical system for making the split members substantially the same, the reflected light beam from the living eye passes through the optical paths of the two projected light beams in reverse, and combines the optical paths with the optical path splitting member, It is characterized in that the reflected light beam from the first measurement object surface and the reflected light beam from the second measurement object surface interfere with each other.

(Action) According to the living eye size measuring device of the present invention, the refractive power correcting optical system uses the wavefront shape of the reflected light beam from the first measurement target surface and the wavefront shape of the reflected light beam from the second measurement target surface. Are made substantially the same by the optical path splitting member, and the number of interference fringes is small or substantially constant, so that observation becomes easy.

Embodiment 1 FIG. 1 shows an optical system of a living eye measuring apparatus according to a first embodiment of the present invention, which is used for measuring an axial length as a living eye dimension.

In FIG. 1, reference numeral 20 denotes a semiconductor laser, reference numeral 21 denotes a collimator lens, and reference numerals 22 and 23 denote beam splitters. The semiconductor laser 20 has a relatively short coherence length of about 0.1 mm. This is because, if a long coherence length is used, interference fringes are obtained even if the optical path difference is largely shifted, and the measurement accuracy of the axial length is reduced. Also, if the coherence length is extremely short, interference fringes cannot be obtained even if the optical path difference is slightly deviated, and it will be difficult to obtain interference fringes.

The laser light emitted from the semiconductor laser 20 is converted into a parallel light beam by the collimator lens 21. This parallel light beam is reflected by a reflecting surface of a beam splitter 22 as an optical path splitting member.
By 24 it is divided into a parallel light flux P ₂ is guided into a parallel light beam P ₁ and the optical path length changing member 25 is guided to the beam splitter 23. The optical path length changing member 25 has reflection surfaces 26 and 27,
It has a function of changing the optical path length of the parallel light beam P ₂ by moving in the arrow direction. When moving the optical path length changing member 25 in the arrow direction by (ΔL / 2), the optical path length of the parallel light beam P ₂ changes by the deviation amount [Delta] L.

The beam splitter 23 has a reflection / transmission surface 28 and functions as an optical path combining member. A refractive power correction lens 29 is provided between the beam splitter 23 and the beam splitter 22. The refractive power correction lens 29 is a beam splitter
22 has the function of guiding the reflection and transmission plane 28 of the beam splitter 23 to parallel light beams P ₁ that has passed through a convergent light beam P ₁ 'to. The parallel light flux P ₂ from the optical path length changing member 25 is guided to the beam splitter 23. This parallel light beam P ₂ is
The parallel light beam P ₂ ′ is reflected by 28 and becomes a parallel light beam P ₂ ′. The parallel light beam P ₂ ′ and the convergent light beam P ₁ ′ are guided to the objective lens 56 via the beam splitter 55. With this objective lens 56, when the eye to be examined is a normal eye, the convergent light beam P ₁ ′ becomes a parallel light beam P ₁ ″,
P ₂ ′ becomes a convergent light beam P ₂ ″ and is guided to the living eye 31. The convergent light beam P ₂ ″ becomes a light beam heading toward the corneal curvature center 40.

The apparatus body is aligned with the living eye 31 using the infrared LED 32, and the CCD camera 34 is used for observing the anterior segment. The infrared light emitted from the infrared LED 32 passes through the condenser lens 36, the pinhole 37, and the relay lens 49, is reflected by the half mirror 33, and is guided to the beam splitter 55. The light beam reflected by the reflection surface 30 of the beam splitter 55 is converted into a parallel light beam by the objective lens 56, and is guided to the living eye 31. The beam splitter 55 has a function of transmitting semiconductor laser light and reflecting other light.

The infrared light is reflected by the cornea 38, which is the first measurement target surface of the living eye 31, passes through the objective lens 56 again, is reflected by the beam splitter 55, passes through the half mirror 33, and forms an imaging lens.
The light passes through 35 and is guided to the CCD camera 34. CCD camera 34
Is connected to a TV monitor 44 described later. Living eye 31
The alignment of the optical system is performed by observing the reflected bright spot of the infrared reflected light beam projected on the TV monitor 44, and the optical system is aligned vertically and horizontally in a plane orthogonal to the optical axis direction of the optical system. by moving the alignment of the optical axis O ₁ of the optical system is performed for the corneal apex P.

When the alignment distance in the optical axis direction of the optical system with respect to the living eye 31 is set such that the convergent light beam P ₂ ″ is incident on the corneal curvature center 40 of the cornea 38 of the living eye 31 as shown in FIG. Then, the convergent light beam P ₂ ″ is reflected by the cornea 38, and the reflected light beam P ₃ is reflected on the original optical path. On the other hand, the parallel light beam P ₁ ″ guided to the living eye 31 is guided as a convergent light beam by the cornea 38 and the crystalline lens 41 to the fundus 42 that is the second measurement target surface.

Then, by moving the power correction lens 29, the spot is formed on the fundus 42, the reflected light beam P ₄ reflected by the fundus 42 is reflected in the optical path original again passes through the lens 41 and the cornea 38 .

Each of the reflected light fluxes P ₃ and P ₄ is guided to the beam splitter 22 through the original optical path (see FIG. 1). The two reflected light beams P ₃ and P ₄ at the beam splitter 22 are plane waves having a substantially flat wavefront shape. Reflected beam P ₄ is reflected by the reflecting surface 24 of the beam splitter 22 and imaging lens 46
, An image is formed on a confocal stop 47, and is guided to a CCD camera 43 as a parallel light beam by a collimating lens 48. CCD
The camera 43 is connected to a TV monitor 44.

The measurement by the living eye measurement device is performed as described below.

First, the axial length of the known reference to the X _0. This reference axial length X ₀ using the average axial length of the living eye 31 (22mm~24mm). Here, when the model eye having the average axial length is arranged at a predetermined position and the optical path length changing member 25 is moved in the direction of the arrow (see FIG. 1), at a predetermined position of the optical path length changing member 25 in the direction of the arrow, It is assumed that interference fringes are projected on the TV monitor 44. The optical path difference of the parallel light beam P ₂ with respect to parallel light beams P ₁ at this time is defined as reference optical path difference L _0. Now, the optical path length to the parallel light beam P ₁ reaches the point K ₁ on the point K ₂ and K ₁ K _2, when a parallel beam P ₂ is reflected at point K _1, point via the optical path length changing member 25 K Assuming that the optical path length up to ₂ is K ₁ K ₃ + K ₃ K ₄ + K ₄ K ₂ , the reference optical path difference L ₀ is L ₀ = (K ₁ K ₃ + K ₃ K ₄ + K ₄ K ₂ −K ₁ K ₂ ) Incidentally, a reference position predetermined position of the optical path length changing member 25 when a reference optical path difference L _0.

Further, assuming that the average refractive index of the living eye 31 is N, the optical path difference based on the reference axial length X ₀ is N · X ₀ , so that the reference optical path difference L ₀
L ₀ = N · X ₀ ... Is established between and the reference axial length X ₀ .

Next, the optical system is aligned with the living eye 31 having the unknown eye axis length X. At this time, it is assumed that no interference fringe is displayed on the TV monitor 44. Then, the optical path length changing member 25 is moved in the direction of the arrow. It is assumed that when the optical path length changing member 25 is moved from the reference position by (ΔL / 2), interference fringes are displayed on the TV monitor 44.

The optical path length based on the axial length X is N · X, and when this is equal to the sum of the reference optical path difference L ₀ and the amount of deviation ΔL, an interference fringe is obtained, so that N · X = L ₀ + ΔL. Become.

Therefore, the unknown axial length X is obtained as X = X ₀ + (ΔL / N) by substituting the equation into the equation and deforming the equation.

By the way, the interference fringe projected on the TV monitor 44 includes the amount of the reflected light beam P ₄ from the fundus 42 and the reflected light beam P ₃ from the cornea 38.
If the light amount is significantly different, the contrast is lowered. This is because the contrast of the interference fringes is best when the amounts of light beams that interfere with each other are equal. Therefore, in this optical system, in order to substantially equal to the amount of the reflected light beam P ₄ from the light quantity and the fundus 42 of the reflected light beam P ₃ from the cornea 38 by controlling the reflectivity of the reflective surface 24 of the beam splitter 22, It is designed so that the reflected light amount of the laser light reflected by the beam splitter 22 is smaller than the transmitted light amount of the laser light passing through the beam splitter 22.
However, since there are individual differences in the living eye 31 may amount of the reflected light beam P ₄ from the fundus 42 is changed in accordance with the individual differences.

Therefore, in this embodiment, the beam splitter 22
Variable density filter 45 between
Is provided. When the contrast of the interference fringes is low, rotate the variable density filter 45 was adjusted such that the amount of the reflected light beam P ₃ from the light quantity and the cornea 38 of the reflected light beam P ₄ from the fundus 42 is substantially the same, the contrast To obtain good interference fringes. When measuring the depth of the anterior chamber and the thickness of the crystalline lens, insert a high refractive power optical path length changing member 50 between the beam splitter 22 and the refractive power correction lens 29,
Performing measurement by shortening the optical path length difference between the parallel light flux P ₁ into a parallel light flux P _2.

When the parallel light flux P ₁ ″ is projected onto the fundus oculi 42, when the refractive power of the living eye 31 is not a normal eye, the reflected light flux P ₄ from the fundus 42 deviates from a plane wave, and the wavefront shape of the reflected light flux P ₄ from the fundus 42 and the wavefront shape of the reflected beam P ₃ from the cornea 38 is not the same. correcting refractive power at this time can be performed by power correction lens 29. that is, the power correction lens 29, living eye 31 in response to power based on the individual difference and the light beam is shifted from the parallel beam P _1, as a small spot on the fundus 42 is formed, i.e., so that both the wavefront shape becomes the same,
The refractive power correction lens 29 is moved and adjusted.

Therefore, the wavefront shape of both reflected light beams is
, They are almost the same and cause interference.

(Embodiment 2) FIG. 3 shows a second embodiment of the living eye size measuring apparatus according to the present invention.
An example is shown in which an interference state between a reflected light beam from the first measurement target surface and a reflected light beam from the second measurement target surface is electrically detected to obtain an unknown eye axis length X. is there.

The optical system of the dimension measuring device shown in FIG.
Instead of providing 3, an aperture 52, an imaging lens 53, and a photodetector 54 as detection means are provided.

The diaphragm 52 has a circular optical aperture 56 at the center. Instead of the circular optical aperture 56, a cross slit for converting the interference light beam into a slit light beam may be provided. The aperture 52 is chosen such that the peak of the interference detection signal S to be described later is moderate, the reflected light beam P ₄ having passed through the aperture 52 is incident on the photodetector 54.

The measurement by the living eye size measuring apparatus according to the second embodiment is performed as described below.

First, like the first embodiment, the optical path length changing member 25 controlled using the known reference axial length X _0, the reference optical path length changing member 25 when obtaining the known reference axial length X ₀ The position is determined in advance.

Then, set the living eye 31 having an unknown axial length X relative to the axial length X ₀ of the reference, moving the optical path length changing member 25 in the direction indicated by the arrow. In response to the movement of the optical path length changing member 25, the photo detector 54 outputs an interference detection signal S as shown in FIG.

That is, as the difference of the optical path length NX corresponding to the unknown axial length X, the optical path difference between parallel beam P ₂ with respect to parallel light beams P ₁ approaches zero, the output of the interference detection signal S from the photodetector 54 of change Is started, and as the difference approaches zero, the peak of the interference detection signal S increases. Then, the optical path length changing member 25 is further moved in the same direction. Then, the difference between the optical path length NX and the optical path difference increases, the peak of the interference detection signal S decreases, and eventually, the change of the interference detection signal S is not detected.

Now, assuming that the time when the change in the interference detection signal S starts to appear is t ₁ and the end time of the change in the interference detection signal S is t ₂ , for example, the measurement of the axial length X between the time t ₁ and the time t ₂ If a value is obtained, the reference optical path difference L _{0 at} the time of tm = (t ₁ + t ₂ ) / 2
By detecting the displacement amount ΔL (equal to the moving distance from the reference position) of the optical path length changing member 25 from the above and performing the calculation based on the following equation, the unknown eye axis length X can be obtained.

_{NX = L 0 + ΔL = L} 0 + ΔL (tm) X = (L 0 + ΔL) / N = X 0 + ΔL / N Note that because of the following reasons of fluctuation occurs in the interference detection signal S.

Since the reflected light flux P ₃ and the reflected light flux P ₄ are guided to a predetermined area of the photodetector 54 via the stop 52, if a bright spot of the interference fringe is located in the predetermined area, the interference detection signal S becomes a positive peak, Negative peaks occur when dark portions of the interference fringes are located.

According to the second embodiment, the reflected light flux from the cornea 38, which is the first measurement target surface, and the second
Since the interference state with the reflected light beam from the fundus oculi 42, which is the measurement target surface, can be detected, the dimensions of the living eye 31 can be measured quickly and accurately.

Further, the confocal aperture 47 is provided to remove noise on the CCD camera 43. This noise is caused by the fact that the reflected light beam P ₃ and the reflected light beam P ₄ from the living eye 31 are not reflected on the original light path of the irradiation light beam P ₁ and the irradiation light beam P ₂ but are reflected light beam P ₃
There is to occur when the optical path or reflected light P ₄ of the reflected beam P ₄ enters the optical path of the reflected light P _3. However, a light beam that has passed through a light path different from the original light path and is related to noise has a different light path length and is not imaged on the confocal stop 47. And the noise is very small.

By the way, in each embodiment, the cornea which is the first measurement target surface
Although the irradiation position on the cornea 38 is set to the center of curvature 40 of the cornea 38, the same result can be obtained even when the irradiation position is set to the vertex P of the cornea 38.

Having described each embodiment, the reference light path difference L ₀ is set to correspond to the lens thickness to the rear surface from the front surface of the lens 41 can be measured the lens thickness of the dimension of the living eye 31. Similarly, the reference light path difference L ₀ is set to correspond to the anterior chamber depth from corneal 38 to the front surface of the lens 41, it is possible to measure the anterior chamber depth.

(Effect) As described above, the living eye size measuring apparatus according to the present invention uses the refractive power correcting optical system to make the wavefront shape of the reflected light beam from the first measurement object surface and the reflected light beam from the second measurement object surface. Since the interference is made substantially the same with the wavefront shape of the optical path dividing member, the number of interference fringes becomes substantially constant and coarse, and good observation of the interference fringes becomes easy.

[Brief description of the drawings]

FIG. 1 is a view showing an optical system of a first embodiment of a living eye size measuring apparatus according to the present invention. FIG. 2 is a diagram showing a reflected light beam from the living eye shown in FIG. FIG. 3 is a diagram showing an optical system of a living eye size measuring apparatus according to a second embodiment of the present invention. FIG. 4 is an explanatory diagram of an interference detection signal output from the photodetector shown in FIG. FIG. 5 is a diagram showing an optical system of a conventional living eye size measuring apparatus. 20: Semiconductor laser (light beam projecting means) 21: Focusing lens (light beam projecting means) 22: Beam splitter (optical path splitting member) 23: Beam splitter (optical path combining member) 25: Optical path length changing member 29 Refractive power correcting lens (Refractive power correcting optical system) 31 Living eye 38 Cornea (first measurement target surface) 42 Fundus (second measurement target surface) 52 Aperture (detection means) 53 …… Imaging lens (detection means) 54 …… Photodetector (detection means)

Claims (3)

(57) [Claims] A light beam having a short coherence length is projected onto a living eye, and a light beam reflected from a first measurement target surface of the living eye and a second light beam are projected on the living eye.
Based on the interference with the light beam reflected from the measurement target surface, the first
In a living eye size measuring device for measuring a dimension from a measurement target surface to the second measurement target surface, a light beam having a short coherence length is projected onto the first measurement target surface and the second measurement target surface. And an optical path splitting member that splits the optical path with the light path splitting member by an optical path splitting member, synthesizes the light path again with an optical path synthesizing member, and projects the light to the living eye. And a refractive power correcting optics for making the wavefront shape of the reflected light beam from the first measurement target surface and the wavefront shape of the reflected light beam from the second measurement target surface substantially the same in the optical path splitting member. A light beam reflected from the living eye passes through the optical path of the two projected light beams in reverse, and an optical path is synthesized by the optical path splitting member.
A size measuring device for a living eye, wherein a reflected light beam from a measurement target surface and a reflected light beam from the second measurement target surface interfere with each other. 2. The apparatus according to claim 1, further comprising a detecting unit for electrically detecting an interference state between the light beam reflected from the first measurement object surface and the light beam reflected from the second measurement object surface. The living eye size measuring apparatus according to claim 1. 3. The light beam projecting means includes an optical path length changing member, and the detecting means includes a photodetector for outputting an interference detection signal, and the detecting means detects an interference of the living eye based on the interference detection signal and the position of the optical path length changing member. 3. The living eye size measuring device according to claim 2, wherein the size is measured.